1. Field of the Invention
The present invention relates to a manufacturing method for obtaining a resin-made roller shaft by injecting a resin material into a die; the molding die; and the resin-made roller shaft.
2. Description of the Related Art
Conventionally, as for a roller shaft which is used for the transportation of paper in a copying machine or a printer, a roller made from rubber has been press-fitted and joined to a metal shaft. In addition, a shaft made from a resin has been used for a roller shaft whose required rigidity is low.
A shape of a key groove or the like is added to a part of an end face of the metal shaft afterward by working, and a post-worked portion has been subjected to plating treatment as a countermeasure for rust prevention.
For this reason, there have been such problems in a weight of a product and a manufacturing cost of the shaft that the weight becomes heavier, an end requires secondary working, and the surface needs to be subjected to plating as rust prevention treatment.
On the other hand, a method of filling a gas into an inner part of a mold when the inner part is filled with a resin, so as to form a hollow structure in the inner part, has been proposed as a method for forming a cylindrical shape in a shaft made from a resin (see Japanese Patent Application Laid-Open No. H08-132467).
In addition, a method of providing a piece in a direction perpendicular to a direction of opening/closing the mold on the end face has been proposed as a method for eliminating a parting line on the end face (see Japanese Patent Application Laid-Open No. 2001-18226).
Furthermore, a method for forming a shape such as a gear on the end face has been proposed (see Japanese Patent Application Laid-Open No. H10-281139).
Problems to be solved by the invention will be described below with reference to FIG. 13 to FIG. 15.
FIG. 3 illustrates a sectional view of a die for molding a resin-made roller shaft therein and a roller shaft, which are viewed from a perpendicular direction to the roller shaft. FIG. 14 and FIG. 15 are views in which a step portion of a parting line in FIG. 3 is enlarged. A fixed-side cavity 1, a movable-side cavity 2 and a molded roller shaft 3 are shown.
As is illustrated in FIG. 13, conventionally, a die for molding a resin-made roller shaft therein is structured so that the parting line is formed between a fixed side and a movable side. For this reason, a step has been formed on the parting line between the fixed side and the movable side, as is illustrated in FIG. 14 and FIG. 15.
As a result, a step and a burr are formed on the parting line also in the roller shaft 3 which has been molded in the die, as is illustrated in FIG. 16. Because of this, the step and the burr which have been formed on the inside roller shaft 3 appear on the surface of a rubber roller 4, after the rubber roller 4 has been press-fitted, and accordingly there has been a problem that the circularity and the cylindricity on the surface of the rubber roller 4 deteriorates, as is illustrated in FIG. 17.